Hydrostatic collapse of carbon and carbon-glass fibre composite tubes involving geometrical and material nonlinearity

This paper describes for the first time, a theoretical investigation into the collapse of forty circular cylindrical composite tubes under external hydrostatic pressure. The investigation of the twenty four composite tubes was on fibre-reinforced plastic tube models, manufactured from a mixture of three carbon fibre layers and two E-glass fibre layers. The material lay-up was 0/90/0/90/0 degrees with the carbon fibres being laid lengthwise (0 degrees) and the E-glass fibres being laid circumferentially (90 degrees). The other sixteen composite tubes were made from carbon fibre models constructed from sixteen carbon layers with different thicknesses. The material lay-up was 0/0/90/90/90/0/90/90/90/90/0/90/90/90/0/0 degrees. The work presented in this paper is of importance for deep diving submarines; especially for those of a large diameter, particularly when subjected to the huge hydrostatic pressures that they have to withstand. The theoretical investigations were carried out using two different finite element computer programs, namely the software program ANSYS 13.0 with graphical displays, and the in-house computer program RCONORTV. The results of the present study were compared with the experimental results carried out in earlier investigations. With the commercial software package ANSYS, two different analyses were carried out; one for the eigen buckling pressure and the other for a non-linear analysis. For the carbon-glass models, the predicted buckling pressure obtained with ANSYS and RCONORTV were higher than the ones obtained with the experimental method. On the other hand, for the carbon fibre models, the resulting analyses were more reliable for both ANSYS and RCONORTV and similar to the experimental results. This paper also provides design charts for all models, using both of the theoretical approaches.